This invention relates to an improvement in an apparatus for cleaning containers being open at one end, particularly seamless metal cans.
A lubricant is applied to seamless metal cans, for example, drawn and ironed cans (hereunder referred to as D & I cans) which are made from sheets of a metal such as aluminum or tinplate by drawing and ironing processings, in the drawing and ironing processings, respectively, for their manufacture, so it is necessary to carry out defatting treatment, that is, to remove said lubricant from the cans, prior to the subsequent steps (chemical treatment step and painting step).
As methods for defatting treatment of D & I cans, there have been known a method for defatting which comprises subjecting cans while moving on a net conveyor upside down to sprays of a defatting treatment liquid from over and below the conveyor and another one for defatting treatment which comprises placing D & I cans in an airtightly closable cell and introducing in the cell a liquid for defatting treatment which is a volatile cleaning liquid such as trichloroethylene.
This invention relates to an improvement in an apparatus for the latter type treatment.
An example of an apparatus for the latter type treatment is disclosed in U.S. Pat. No. 4,026,311 specification.
In the accompanying drawings, FIG. 1 is a sectional view of the apparatus forming the cell for defatting treatment of seamless cans shown in said U.S. patent specification, and FIG. 2 is an enlarged view of the A portion of FIG. 1.
The apparatus shown in FIG. 1, that is, a pot assembly, comprises a support plate 36 secured to a top plate (not shown) by a securing means; an upright cylindrical shell 38 mounted on this support plate 35, the top of the shell being open and the bottom having an end wall 39 formed with a central aperture 40; a centering ring 41 mounted on said end wall 39; and a cylindrical core 42 mounted on said ring 41, the bottom of the core having a spigot 43 which extends as a close fit through said centering ring 41 and said aperture 40, and the bottom of this spigot 43 being seated in a recess in the support plate 36. Screws 45 extend upwards through the support plate 36, the end wall 39 and the ring 41, and are screwed into the core 42 thereby securely clamping the components together. The core 42 co-operates with the shell 38 to form a cavity 46 for the reception of a container X (shown by a two-dotted chain line) to be treated for defatting. A recess is formed in the center area of the top of the core 42, and a duct 49 extends from the recess downwards through the core 42 and the spigot 43 and connects with a duct 50 in the support plate 36. These ducts 49 and 50 form a first passage for treating fluid (inlet passage). Sealing rings 51 and 52 are mounted in grooves in the bottom surfaces of the shell 38 and the spigot 43, respectively. The centering ring 41 has an outer surface which is aligned with the outer surface of the core 42, and the centering ring 41 is provided with many axially extending fins 54 spaced around the ring, the fins 54 being adapted to engage inside the mouth of a container fed open-end downwards onto the core 42 so as to fix co-axially the container to the core 42, and each fin 54 is formed with a ledge 55 for the support of a container. The inside diameter of the upper end part 56 of the shell 38 is larger than that of the other part of the shell, and the inner surface 57 of the shell immediately below said part 56 is tapered downwardly.
The pot assembly described in this U.S. patent includes a lid 58 consisting of a cover plate 60; a crown 61 located in a recess in the underside of the plate 60 and having an annular peripheral flange 63 formed with a downwardly projecting lip 64, the crown being secured to the cover plate 60 by screws 65; and an annular sealing member 66 having a radical wall 67 clamped between the flange 63 and the cover plate 60, and a cylindrical wall 68 extending downwards below the lip 64. The crown 61 is formed with a central aperture 70 aligned with an aperture 71 in the cover plate 60, the upper portion of the aperture 70 being enlarged to form a valve chamber 72 housing a valve member 73 having a stem 74 slidably mounted in the lower portion of the aperture 70.
The valve member 73 is adapted to block the flow of fluid through the apertures 70 and 71 when in a closed position in which it is engaged against the bottom wall 75 of the valve chamber by a spring 76 compressed between the valve member 73 and a tubular pipe connector 77 screwed into the aperture 71. The fluid can flow through the apertures 70 and 71 when the valve member 73 is in an open position spaced from the wall 75 of the valve chamber. These apertures 70 and 71 form a second passage for treating fluid (outlet passage). The cover plate 60 is secured to a sleeve 80 which is movable up and down and is rotatable.
In order to subject seamless cans with a lubricant adhering thereto to defatting treatment using the pot assembly, first the sleeve 80 is operated to lift the cover plate 60 to a position at which the lower end portion of the crown 61 rigidly secured to the cover plate becomes higher than the upper end of the cylindrical shell 38, and then the cover plate 60 is rotated around the sleeve 80 so that the can X may be inserted in the cavity 46 defined by the shell 38, the core 42 and the centering ring 41. After the can X is inserted in the cavity 46, the cover plate 60 is rotated around the sleeve 80 and then moved down to airtightly close the cavity 46 with the crown 61.
Here, the gap between the shell 38 and the crown 61 is kept in a sealed state through the annular sealing member 66 composed of an elastic material. Next, a defatting liquid such as trichloroethylene is injected via the first passage for treating fluid. The injected defatting liquid moves up through the duct 50 and then the duct 49, makes headway between the inner surface of the bottom of the can X and the top surface of the core 42, flows down between the inner surface of the body of the can X and the outer surfaces of the core 42 and the centering ring 41, passes through between the respective fins 54 of the centering ring 41, moves up between the outer surface of the body of the can X and the inner surface of the shell 38, makes headway between the outer surface of the bottom of the can X and the inner surface of the crown 61 and then is discharged through the ducts 70 and 71 composing the second passage for treating fluid. During this time, said inner and outer surfaces of the can X is cleaned with the trichloroethylene. Then, detergent-containing water is injected through the first passage for treating fluid to clean said both surfaces of the can X with the detergent-containing water. Last, air at a high temperature is injected through the first passage for treating fluid to dry the cavity (in which the can X is placed).
The foregoing method for defatting treatment requires the use of water and the use of a volatile cleaning liquid, and thus the method has drawbacks in that the long time necessary for the drying keeps the defatting treatment time from being shortened satisfactorily, and the treatment cost is high as it is hard to reuse the fluid after the treatment.
In order to apply a defatting treatment method, which is carried out in the field of metal processing other than for can manufacture, that is, a two-step defatting treatment method where pre-wash with treating fluid in a liquid state is first carried out, and then wash proper using the same type treating fluid in a vapor state, is effected, to the defatting treatment of D & I cans using a pot assembly of the above U.S. patent without being accompanied by the above-mentioned drawbacks, the inventors of the present invention subjected D & I cans to defatting treatment in the following order of steps.
That is, a can is inserted in the cavity in a pot assembly as shown in FIG. 1,
(1) first, both the inner surface and the outer surface of the can are preliminarily defatted with methylene chloride in a liquid state while it is injected through the first passage for treating fluid and discharged via the second passage for treating fluid;
(2) then, gaseous methylene chloride is injected under pressure through the first passage for treating fluid to defat both the inner surface and the outer surface of the can with the gaseous methylene chloride while discharging the liquid methylene chloride adhering to the surface of the can in and the wall of the cavity;
(3) after that, methylene chloride in a liquid state purified by distillation is injected through the first passage for treating fluid to subject both the inner surface and the outer surface of the can to defatting proper until it is discharged via the second passage for treating fluid;
(4) the same treatment as in the above (2) is repeated;
(5) the methylene chloride adhering to the surface of the can and the wall of the cavity is removed by vacuum suction through each of the first and second passages for treating fluid, and at the same time the cavity is dried;
(6) thereafter, the methylene chloride in the cavity is completely removed by pressurized air injected through the first passage for treating fluid; and
(7) then, the crown is lifted and rotated to open the cavity and to take out the can.
The complete removal of the methylene chloride from the cavity is a necessary step for the prevention of the loss of the volatile cleaning liquid and for the prevention of the release of the gaseous fluid into the air which it might damage human bodies.
Here, the defatting treatment consisting of the above steps is carried out by injecting treating fluid into the cavity of the pot assembly and charging said fluid out of said cavity in such a manner that the above respective steps are effected successively while said pot assembly is transferred along a predetermined passageway.
The degree of defatting of cans subjected to defatting treatment consisting of the above steps was examined to find that the lubricant still adheres here and there on the surfaces of the cans which must have surely been subjected to the defatting treatment. If the lubricant adheres to the surfaces of cans, one fails in complete chemical treatment of the surfaces of such cans in the subsequent step, and they will be judged to be rejects for their poor resistance to rust and poor adhesion of paint.
In order to find the reason why the lubricant adheres to the cans, we further made experiments for examination to reveal that the adhesion is attributable to the apparatus.
That is, as is clearly understood from FIG. 2, the upper portion of the shell 38 has a recessed tapered portion 57, and the cylindrical wall 68 of the annular sealing member 66 extends downward to the upper portion of this tapered portion 57 to form a pocket. As arrows show, aqueous methylene chloride moves up between the outer surface of the can X and the inner side wall of the shell 38 cleaning the surfaces of the cans, and a part of the fluid enters the above pocket. This part of the fluid which contains a part of the lubricant washed off from the surfaces of the cans therewith is left in said pocket (said part of the fluid and that of the lubricant remain adhering to the surface of the tapered portion of the shell 38 and the end surface of the cylindrical wall 68 of the annular sealing member 66), and the remaining fluid is discharged.
This part of the lubricant (more particularly, the lubricant in admixture with the methylene chloride) still remains adhering to the pocket portion without being completely wash off even after the passing of gaseous methylene chloride, and adheres to the outer surfaces of the cans by suction when the vacuum treatment in the above step (5) is carried out.